HADLEY — An odor of natural gas at the Mountain Farms Mall on Route 9 forced a short-term evacuation of Wal-Mart and Barnes & Noble Thursday afternoon, but upon investigation no gas leak was found.

The odor report came in around 2 p.m. and caused the side-by-side stores to be cleared out for about 30 minutes, said David Fleming, a spokesman at WS Development, the Chestnut Hill owner of the mall.

Several people on HampScanner’s Facebook page, which monitors and reports on local police scanner action, said the mall and nearby stores were evacuated, but people were seen entering shops a short time later.

According to Chris Farrell, a spokesman for Berkshire Gas, the company was first alerted to the odor by a Pier 1 employee who said there was “activity” at Wal-Mart. Although neither Wal-Mart or the Hadley Fire Department notified the gas company, Berkshire Gas employees were dispatched to the scene.

“Our personnel investigated and did not find a gas leak,” Farrell wrote in an email to the Gazette.

Farrell cited an exhaust odor from a rooftop heating unit that was being “improperly operated.” Berkshire Gas shut gas off to the unit and will not restore it until repairs are made, he said.